Process for producing carotenoid emulsions

ABSTRACT

A process for producing a carotenoid emulsion characterized by passing a suspension of a carotenoid in toluene through a heated pipe at such a rate as to result in a residence time of 10 to 600 seconds to thereby heat the suspension to 50 to 120° C. and dissolve the carotenoid, immediately mixing the resultant solution with water having a temperature of 5 to 60° C. in the presence of an emulsifying agent to form an emulsion, and distilling off the toluene under vacuum. By the process, an emulsion containing a carotenoid as an active ingredient can be easily and industrially advantageously produced with satisfactory productivity while maintaining a high proportion of wholly trans molecules in the carotenoid.

TECHNICAL FIELD

This invention relates to a process for producing a carotenoid emulsion.

BACKGROUND ART

Carotenoids are broadly present in nature, and widely used as colorantsfor food, etc. utilizing the characteristic that they have yellow to redcolor. Some carotenoids are also known to show provitamin A activity,cancer-inhibiting effect or the like, and are a compound group drawingattention also from a pharmacological viewpoint. Many isomers arepresent in carotenoids based on many carbon-carbon double bonds whichthey possess, and when a use as colorants or a use as a physiologicallyactive agent such as a provitamin A active agent is considered,carotenoids having a high all trans-form proportion are preferred.

Carotenoids are compounds which are in a crystalline state at ordinarytemperature and have a high melting point, are insoluble in water,extremely low in solubility in organic solvents or fats and oils, and,moreover, tend to be isomerized with heat, and tend to be readilydenatured with oxygen or light. Therefore, when it is intended to usecarotenoids as colorants for food or physiologically active agents, theyneed to be processed into stable and readily utilizable forms. As oneprocess for it, there is a process of producing an emulsion of acarotenoid by mixing a solution of the carotenoid in an organic solventor fat or oil with water in the presence of an emulsifier.

Known processes of producing an emulsion of a carotenoid include

(1) a process which comprises emulsifying a solution of a carotenoid ina volatile water-immiscible solvent such as a halogenated hydrocarbon orcarbon disulfide, into an aqueous solution of a colloid having swellingproperties; and removing the volatile solvent from the resultingemulsion (see JP-A-37-12428),

(2) a process which comprises emulsifying a super-saturated solution ofa carotenoid in an edible oil which is liquid at about 20 to 40° C.,which solution is heated to 100 to 160° C. into an aqueous gelatinsubstance solution (see U.S. Pat. No. 2,861,891),

(3) a process which comprises mixing a solution of a carotenoid in avolatile organic solvent such as a halogenated hydrocarbon with anaqueous solution containing sodium lauryl sulfate or the like, whileremoving the volatile organic solvent (see JP-A-51-41732 andJP-A-52-84232),

(4) a process which comprises rapidly dissolving a carotenoid, togetherwith an edible oil of 1.5 to 20 times the mass of the carotenoid and anappropriate amount of an emulsifier, in a volatile organic solventmiscible with water at a temperature of 50 to 240° C., and thenimmediately mixing the resulting solution with an aqueous solution of aprotective colloid at a temperature of 0 to 50° C. to move thehydrophilic solvent components into the aqueous phase, and at that timechanges the hydrophobic oil phase containing and dissolving thecarotenoid to a fine dispersion phase (see JP-A-63-196242),

(5) a process which comprises contacting a suspension of a carotenoid ina high boiling oil with superheated steam for 30 seconds at most andemulsifying the resulting mixture in an aqueous solution of a colloid(see JP-A-3-66615),

(6) a process which comprises heating trans-form β-carotene, fats oroils and limonene to make a solution, recovering the limonene andconverting the resulting fat or oil layer dissolving the trans-formβ-carotene to an emulsion in the presence of an emulsifier (seeJP-A-8-119933),

(7) a process which comprises feeding a suspension of a carotenoid in awater-immiscible organic solvent into a heat exchanger for a residencetime of less than 5 seconds to heat the suspension to 100 to 250° C.,rapidly mixing the resulting solution with an aqueous solution of easyto swell colloid at a temperature in the range of 20 to 100° C., andthen removing the organic solvent (see JP-A-2000-186224),

(8) a process which comprises heating a suspension of a carotenoid in ahigh boiling organic liquid by passing the suspension through a conduitof 0.1 to 50 mm inside diameter heated to a temperature in the range of120 to 700° C. for a residence time of 0.05 to 5 seconds to dissolve thecarotenoid, and then immediately adding the resulting solution into anaqueous solution containing an emulsifier to emulsify the solution (seeJP-A-2002-302479), and

(9) a process which comprises mixing a suspension of a carotenoid in ahigh boiling organic liquid with a high boiling organic liquid heated toa temperature in the range of 120 to 500° C. for a time of 0.05 to 10seconds, to dissolve the carotenoid, and then immediately adding theresulting solution into an aqueous solution containing an emulsifier toemulsify the solution (see JP-A-2002-316924).

DISCLOSURE OF INVENTION

The processes of the above (1) and (3) have a problem that although anorganic solvent having comparatively high solubility on carotenoids evenat ordinary temperature such as a halogenated hydrocarbon, e.g.chloroform or carbon disulfide is used, these solvents have hightoxicity and severe control has recently been required on their use fromthe viewpoint of an environmental problem, and thus they are hard to useindustrially. The process of the above (2) has a problem to beeconomically disadvantageous because the visible absorption spectrum ofdry powder of carotenoid obtained from the resulting emulsion gets low,and for example in the case of using the dry powder as a colorant forfood, the use quantity of the dry powder needs to be increased to obtaina desired value of color strength. The processes of the above (4) and(7) have the problems that since the organic solvent to be used isunnecessary for the final product, it needs to be removed and that useof a large quantity of the organic solvent is needed, which lowersproductivity. The process of the above (5) has the problems that itneeds expensive apparatuses because superheated steam being hightemperature and high pressure is used and further that since wateroriginating in the superheated steam, in addition to the water containedin the aqueous solution of the colloid, joins the resulting emulsion,when the production of carotenoid powder from the emulsion is intended,a large quantity of water needs to be removed. The process of the above(6), wherein limonene is used in view of inhibiting isomerization oftrans-form β-carotene when the trans-form β-carotene is heated fordissolution, has the problems that the same quantity or more of thelimonene as that of the fat or oil needs to be used and further thatsince limonene is not needed in the final product, a step to remove itis indispensable, and moreover that the total all trans-form proportionof β-carotene in the resulting emulsion is as low as on the order of 60to 67%. As to the processes of the above (8) and (9), large-scaleancillary facilites for generating high temperature are necessary, and,in that view, these processes have room to be improved.

Thus, the object of the invention lies in providing a process capable ofproducing an emulsion containing a carotenoid as an effective ingredientwith the total all trans-form proportion of the carotenoid maintainedhigh, with good productivity, conveniently, and industriallyadvantageously.

The present inventors have made intense researches for accomplishing theabove object. As a result, we found that, by using a process of passinga suspension of a carotenoid in toluene through a heated conduit for ashort time, to heat the suspension to a temperature in a particularrange and dissolve the carotenoid; immediately adding the resultingsolution into an aqueous solution of a temperature in a particular rangecontaining an emulsifier to give an emulsion; and then distilling offthe toluene under reduced pressure, a carotenoid emulsion not containingthe unnecessary organic solvent and a large quantity of water can beproduced as a final product. We further found that carotenoid powderobtained by spray drying a carotenoid emulsion obtained by such aprocess or by stirring the carotenoid emulsion in a nonpolar solvent tomake the emulsion particles, and filtering and drying the particles canbe used as colorants for food or a physiologically active agent, andcompleted the invention.

Namely, the present invention relates to

<1> a process for producing a carotenoid emulsion which comprisesheating a suspension of the carotenoid in toluene (hereinafter merelyreferred to as “carotenoid suspension”) to a temperature in the range of50 to 120° C., by passing the suspension through a heated conduit for aresidence time of the range of 10 to 600 seconds, to dissolve thecarotenoid, immediately mixing the resulting solution with water of atemperature in the range of 5 to 60° C. in the presence of an emulsifierto emulsify the solution, and then distilling off the toluene underreduced pressure, and

<2> carotenoid powder obtained by spray drying the resulting carotenoidemulsion obtained in <1>, or by stirring the carotenoid emulsion in anonpolar solvent to make the emulsion particles, and filtering anddrying the particles.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an embodiment of the production process of the invention.In FIG. 1 the symbols have the following meanings, respectively.

-   1 Feed vessel (equipped with an agitator)-   2 Metering pump-   3, 7, 10 Thermometer-   4 Conduit-   5 Vessel containing a heat medium-   6 Heating apparatus-   8 Cock-   9 Preparation vessel (equipped with a homogenizer)-   11 Manometer-   12 Piping for distilling-off-   13 Condenser-   14 Receiver-   15 Vacuum pump

BEST MODE FOR CARRYING OUT THE INVENTION

As carotenoids used in the invention, there can be exemplifiedα-carotene, β-carotene, canthaxanthin, astaxanthin, apocarotenal,citranaxanthin, cryptoxanthin, lycopene, zeaxanthin, etc. Thesecarotenoids can be used alone or as a mixture of two or more. As to theform of carotenoids used, in view of smoothly carrying out thedissolution of the carotenoids in toluene, it is preferred that thecarotenoids are crystals having a particle size of 50 μm or less and itis further preferred that the carotenoids are crystals having a particlesize of 15 μm or less.

A solvent used to obtain a carotenoid suspension in the invention istoluene. Toluene has an advantage that the solubility of carotenoids init is largely different between at ordinary temperature and at the timeof heating.

Carotenoids are sensitive to oxygen, and therefore it is preferred toadd an antioxidant in preparation of a carotenoid suspension. As theantioxidant, there can, for example, be mentioned t-butylhydroxyanisole,t-butylhydroxytoluene, vitamin E, ethoxyquin, etc., and vitamin E isparticularly preferred. The antioxidant can be mixed with toluene at anyproportion and used, but it is, usually, preferred to use theantioxidant in the range of 10 times or less the mass of the carotenoidused.

There is no particular limitation on the proportion of the carotenoid totoluene in preparation of a carotenoid suspension, but, in view of thesolubility of the carotenoid, productivity and the like, the usequantity of carotenoid is preferably in the range of 0.1 to 10% by mass,more preferably in the range of 0.5 to 5% by mass, based on the toluene.

According to the invention, first, the carotenoid suspension is heatedin a short time by passing the suspension through a heated conduit, todissolve the carotenoid.

The heating temperature and heating time of the carotenoid suspensionmay vary depending on the kind of the carotenoid composing thesuspension, the use proportion of the carotenoid to toluene, the passingquantity and passing rate of the suspension, etc., but in view ofinhibiting isomerization of the carotenoid with heat, it is necessarythat the heating temperature is in the range of 50 to 120° C. and theheating time is in the range of 10 to 600 seconds, and it is preferredthat the heating temperature is in the range of 60 to 110° C. and theheating time is in the range of 10 to 30 seconds.

The heating temperature of the conduit may vary depending on the kind ofthe carotenoid composing the suspension to be passed, the use proportionof the carotenoid to toluene, the passing quantity and passing rate ofthe suspension, etc., but, usually, the heating temperature ispreferably in the range of 50 to 200° C. and more preferably in therange of 70 to 150° C.

As means for heating the conduit, ordinary heating means can be adoptedsuch as a method to use a gas burner, an electric heater,electromagnetic induction or the like; a method to heat the conduit byusing an organic heating medium such as a usual heating medium oil or aninorganic heating medium such as HTS (Heat Transfer Salt: mixture ofsodium nitrite, sodium nitrate and potassium nitrate); and a method touse a high temperature gas such as steam or heated air.

The material of the conduit is not particularly limited so long as it isusable in the process of the invention, and includes, for example metalssuch as iron, stainless steel and titanium, glasses, etc. As to theshape of the conduit, any shape can be adopted, and examples thereof arelinear conduits, conduits of a coil shape, etc. Further, in view offurther improving productivity, it is also possible to use pluralconduits with parallel connection.

In the process of the invention, the inside diameter of the conduit tobe used is not particularly limited, but, usually, is preferably in therange of 0.1 to 500 mm and more preferably in the range of 0.5 to 100mm. When a thin conduit of which inside diameter is less than 0.1 mm isused, clogging is liable to occur in the conduit when the carotenoidsuspension is passed, and on the other hand, when a conduit having aninside diameter of more than 500 mm is used, it gets very hard to heatthe carotenoid suspension, in a short time, to such a temperature thatthe carotenoid dissolves in toluene.

As to the thickness of the conduit, there is no particular limitation,but in view of efficiently supplying quantity of heat to the carotenoidsuspension and in view of withstanding the pressure given to the conduitwhen the suspension is passed, the thickness of the conduit is, usually,preferably in the order of 1/10 to 10 times the inside diameter of theconduit, more preferably in the order of ⅕ to 5 times the insidediameter.

The length of the conduit of the part heated within the prescribed rangemay vary depending on the kind of the carotenoid composing thecarotenoid suspension to be passed, the use proportion of the carotenoidto toluene, the passing quantity and passing rate of the suspension,etc., but, in view of supplying enough heat quantity to dissolve thecarotenoid in toluene within the time for the carotenoid suspension topass through the conduit and in view of inhibiting the isomerization ofthe carotenoid with heat as completely as possible during the time, thelength of the conduit of the part is, usually, preferably in the rangeof 0.1 to 20 m, more preferably in the range of 0.5 to 10 m.

As means for transferring the carotenoid suspension to the conduit ofthe part heated to the prescribed temperature, means usually used whenliquid is transferred, such as metering pumps and compressed gases, canbe used. The amount of the carotenoid suspension to be transferred mayvary depending on the kind of the carotenoid composing the suspension tobe passed, the use proportion of the carotenoid to toluene, the heatingtemperature of the conduit, and the heating time of the suspension,etc., but the amount is, usually, preferably in the range of 0.1 to 10kg/minute.

There is no particular limitation on the size and length of the conduitup to introduction of the carotenoid suspension into the inlet of theheated conduit part. On the other hand, the length of the conduit fromthe outlet of the heated conduit part to the emulsifying apparatus, is,usually, preferably in the range of 0.01 to 20 m in view of inhibitingthe isomerization of the carotenoid with heat, etc.

Advantageously, it is, for example, possible to use tubes of the samematerial and the same diameters as the conduit from the feed vesselcharged with the carotenoid suspension to the introduction part of theheated conduit, the heated conduit and the conduit from the heatedconduit to the emulsifying apparatus.

As mentioned above, by passing the carotenoid suspension through theheated conduit, a solution wherein the carotenoid is in a state of beingdissolved in toluene (hereinafter, referred to as “carotenoid solution”)can be prepared, and the solution is then immediately subjected to astep of mixing with water, in the presence of an emulsifier, to emulsifythe solution.

As to the emulsifier, there is no particular limitation so long as it iscapable of emulsifying the carotenoid solution and water, and there can,for example, be mentioned fatty acid esters of ascorbic acid such asascorbic acid palmitate and ascorbic acid monooleate; sucrose fatty acidesters such as sucrose palmitate and sucrose monooleate; sorbitan fattyacid esters such as sorbitan palmitate and sorbitan monooleate;polyglycerol fatty acid esters such as polyglycerol palmitate andpolyglycerol monooleate; etc. Among them, it is particularly preferredto use fatty acid esters of ascorbic acid such as ascorbic acidpalmitate. The emulsifier may be added into the water in advance, or maybe mixed into the carotenoid suspension or the carotenoid solution. Whena fatty acid ester of ascorbic acid is added into the water in advance,a basic alkali metal compound such as sodium hydroxide or sodiumcarbonate may be added in order to make the dissolution of the fattyacid ester of ascorbic acid easy.

The use amounts of the emulsifier and the water are not particularlylimited so long as the carotenoid solution can be emulsified, namely astable O/W emulsion can be formed. But, usually, the use amount of theemulsifier is preferably in the range of 0.05 to 15% by mass, morepreferably in the range of 0.1 to 5% by mass, based on the water used.The use amount of the water may vary depending on the kind of thecarotenoid, the use proportion of the carotenoid to toluene, etc., butis preferably in the range of 1 to 2,000 times the mass of thecarotenoid, more preferably in the range of 10 to 500 times the mass ofthe carotenoid.

In view of improving the stability of the carotenoid emulsion to beproduced, gelatin, sugars, gum arabic, starches or the like may be addedinto the water. As the sugars, there can be mentioned sucrose, invertsugar, etc.

At the time when the carotenoid solution is mixed with water in thepresence of the emulsifier to emulsify the solution, the temperature ofthe water is needed to be in the range of 5 to 60° C., and is preferablyin the range of 30 to 50° C. When the temperature of the water is lessthan 5° C., the emulsion state gets bad, and when it is more than 60°C., the quality of the carotenoid solution gets bad.

The step to mix the carotenoid solution with water, in the presence ofan emulsifier, to emulsify the solution can be carried out, for example,by a process of charging an aqueous solution of the emulsifier inadvance into a vessel equipped with an agitation-type emulsifier, andthen adding the carotenoid solution thereinto intermittently orcontinuously to emulsify the solution; a process of charging water inadvance into a vessel equipped with an agitation-type emulsifier, andthen adding thereinto the carotenoid solution containing the emulsifierintermittently or continuously to emulsify the solution; a process ofintroducing the carotenoid solution and the aqueous solution of theemulsifier together into a line mixer to emulsify the solution; aprocess of introducing the carotenoid solution containing theemulsifier, and water together into a line mixer to emulsify thesolution; etc.

Then, a step to distill off the toluene under reduced pressure, from anemulsion of the carotenoid containing toluene, obtained by mixing thecarotenoid solution with water in the presence of the emulsifieraccording to a process as mentioned above, is carried out.

The temperature at which the toluene is distilled off is preferably inthe range of 5 to 60° C., more preferably in the range of 30 to 50° C.As to the degree of reduced pressure in the distilling-off of thetoluene, such a degree of reduced pressure can appropriately be selectedthat the distilling-off of the toluene is possible within the abovetemperature range. The distilling-off of the toluene is carried outuntil toluene comes not to exist in the emulsion of the carotenoid.Since toluene is distilled off as an azeotrope with water, it is alsopossible to separate the distilled water from the toluene and bring itback to the carotenoid emulsion.

It is also possible to carry out the step of mixing the carotenoidsolution with water in the presence of the emulsifier to emulsify thesolution and the step of distilling off toluene under reduced pressurefrom the carotenoid emulsion containing toluene, at the same time.

The process of the invention is a series of operations comprising anoperation of heating a carotenoid suspension to a temperature in therange of 50 to 120° C. by passing the suspension through a heatedconduit for a residence time in the range of 10 to 600 seconds, todissolve the carotenoid; an operation of immediately mixing theresulting solution with water of a temperature in the range of 5 to 60°C., in the presence of an emulsifier, to emulsify the solution; and anoperation of distilling off toluene under reduced pressure, and acarotenoid emulsion can be obtained with such convenient operations.

The obtained carotenoid emulsion can be used as it is for a use such asa colorant for food or a feed additive. Further, by spray drying thecarotenoid emulsion, or by stirring the carotenoid emulsion in anonpolar solvent such as hexane, toluene or a paraffin, to convert thecarotenoid emulsion to particles, and filtering and drying theparticles, powder containing the carotenoid can be obtained. Thecarotenoid powder can be used for uses such as a colorant for food and aphysiologically active agent.

EXAMPLES

The present invention is specifically described below through examples,but the invention is not limited at all by these examples.

An embodiment of the production process of the present invention isshown in FIG. 1. A carotenoid suspension and an emulsifier are chargedinto Feed vessel 1. The carotenoid suspension containing the emulsifieris fed from Feed vessel 1 into Conduit 4 immersed in a heating medium inVessel 5 heated by Heating apparatus 6, via Metering pump 2, and therebythe suspension becomes, in the heated Conduit 4, such a solution thatthe carotenoid is in a state of being dissolved in the toluene. Thissolution is immediately intermittently or continuously fed intoPreparation vessel 9. Vacuum pump 15 can reduces the pressure up toPreparation vessel 9, and toluene, distilled off under reduced pressurefrom the carotenoid emulsion containing toluene prepared in Preparationvessel 9, is recovered into Receiver 14 via Piping for distilling-off 12and Condenser 13.

Example 1 Production of β-Carotene Emulsion

In FIG. 1, as Conduit 4 was used such a coil-shaped stainless steelconduit that the inside diameter is 2 mm, the outside diameter is 3 mmand the length is 4 m. This Conduit 4 was put in Vessel 5 containing aheat medium and heated to 90° C. 700 g of water and 35 g of sucrose wereput in Preparation vessel 9, and 30 g of gelatin was put therein, thenthe mixture was stirred at 40° C. to dissolve the gelatin, and then 15 gof 1N aqueous sodium hydroxide solution was added so that the pH became7 to 8. Separately, 28 g of β-carotene, 1,400 g of toluene, 5.6 g ofascorbic acid palmitate and 5.6 g of vitamin E were put in Feed vessel 1and stirred mildly. The pressure from Preparation vessel 9 to Receiver14 was reduced to 13.3 kPa (100 mmHg) by Vacuum pump 15, the homogenizerof Preparation vessel 9 was operated at 9,000 r.p.m., and the suspensionin Feed vessel 1 was transferred to Preparation vessel 9 at a flow rateof 18 g/minute by Metering pump 2. At that time, the residence time ofthe feed liquid in the heated Cnduit 4 was about 36 seconds, thetemperature of the β-carotene solution at the outlet of the heatedConduit 4 was 86° C., and there was almost no crystals of β-caroteneremaining undissolved.

The feed of the suspension of Feed vessel 1 was continued while tolueneand water distilling in a short time after the start of feed werereceived in Receiver 14, but, three times during the operation, the feedof the suspension was temporarily stopped, and after the liquid quantityin Preparation vessel 9 became appropriate, the feed was restarted.Water collected in Receiver 14 was removed at times, and afterseparation from toluene, brought back to Preparation vessel 9. Theβ-carotene suspension in Feed vessel 1 was used up in 7 hours after thestart of feed, but the distillation operation was continued, and, afteradditional 5 hours, after confirming that the quantity of toluene inPreparation vessel 9 became 0.1% or less, holding the reduced pressurefrom Preparation vessel 9 to Receiver 14 was stopped and the stirring bythe homogenizer was stopped. When the resulting orange emulsion (760 g)was analyzed, this emulsion contained 3.6% of β-carotene and its totalall trans-form proportion was 90%.

Example 2 Production of Canthaxanthin Emulsion

The same apparatus as in Example 1 was used, and the temperature of theheat medium was made to 95° C. 700 g of water and 35 g of sucrose wereput in Preparation vessel 9, and 30 g of gelatin was put therein, thenthe mixture was stirred at 40° C. to dissolve the gelatin, and then 15 gof 1N aqueous sodium hydroxide solution was added so that the pH became7 to 8. Separately, 28 g of canthaxanthin, 1,400 g of toluene, 5.6 g ofascorbic acid palmitate and 5.6 g of vitamin E were put in Feed vessel 1and stirred mildly. The pressure from Preparation vessel 9 to Receiver14 was reduced to 13.3 kPa (100 mmHg) by Vacuum pump 15, the homogenizerof Preparation vessel 9 was operated at 9,000 r.p.m., and the suspensionin Feed vessel 1 was transferred to Preparation vessel 9 at a flow rateof 16 g/minute by Metering pump 2. At that time, the residence time ofthe feed liquid in the heated Conduit 4 was about 41 seconds, thetemperature of the canthaxanthin solution at the outlet of the heatedConduit 4 was 90° C., and there was almost no crystals of canthaxanthinremaining undissolved. Feed and distillation operations were carried outin the same way as in Example 1, and when the resulting orange emulsion(763 g) was analyzed, this emulsion contained 3.5% of canthaxanthin andits total all trans-form proportion was 85%.

Example 3 Production of Astaxanthin Emulsion

The same apparatus as in Example 1 was used, and the temperature of theheat medium was made to 108° C. 700 g of water and 35 g of sucrose wereput in Preparation vessel 9, and 30 g of gelatin was put therein, thenthe mixture was stirred at 40° C. to dissolve the gelatin, and then 15 gof 1N aqueous sodium hydroxide solution was added so that the pH became7 to 8. Separately, 28 g of astaxanthin, 2,000 g of toluene, 5.6 g ofascorbic acid palmitate and 5.6 g of vitamin E were put in Feed vessel 1and stirred mildly. The pressure from Preparation vessel 9 to Receiver14 was reduced to 13.3 kPa (100 mmHg) by Vacuum pump 15, the homogenizerof Preparation vessel 9 was operated at 9,000 r.p.m., and the suspensionin Feed vessel 1 was transferred to Preparation vessel 9 at a flow rateof 16 g/minute by Metering pump 2. At that time, the residence time ofthe feed liquid in the heated Conduit 4 was about 45 seconds, thetemperature of the astaxanthin solution at the outlet of the heatedConduit 4 was 103° C., and there was almost no crystals of astaxanthinremaining undissolved. Feed and distillation operations were carried outin the same way as in Example 1, and when the resulting orange emulsion(736 g) was analyzed, this emulsion contained 3.7% of astaxanthin andits total all trans-form proportion was 84%.

Comparative Example 1 Production of Canthaxanthin Emulsion (Under theCondition of Not Using a Conduit for Heating)

700 g of water and 35 g of sucrose were put in Preparation vessel 9 inFIG. 1, and 30 g of gelatin was put therein, then the mixture wasstirred at 40° C. to dissolve the gelatin, then 15 g of 1N aqueoussodium hydroxide solution was added so that the pH became 7 to 8, andthe homogenizer of Preparation vessel 9 was operated at 9,000 r.p.m. Onthe other hand, 28 g of canthaxanthin, 1,400 g of toluene, 5.6 g ofascorbic acid palmitate and 5.6 g of vitamin E were put in athree-necked flask of content volume 3,000 ml equipped with a refluxcondenser, and the mixture was heated under stirring with a heat mediumbath of 130° C., and held under a condition of reflux of toluene for 15minutes to make the canthaxanthin dissolve. Then, the whole quantity ofthe resulting toluene solution of canthaxanthin was immediately pouredall at once into Preparation vessel 9. In this connection, there wasalmost no crystals of canthaxanthin remaining undissolved in the toluenesolution poured. After the stirring with the homogenizer was continuedfor 30 minutes, the same operation for distillation of toluene and wateras in Example 1 was carried out, and when the resulting orange emulsion(780 g) was analyzed, this emulsion contained 3.5% of canthaxanthin andits total all trans-form proportion was 38%.

INDUSTRIAL APPLICABILITY

Carotenoids which are broadly used as coloring agents for food and useof which from a pharmacological viewpoint is also considered, areneeded, in view of solubility and stability, to be processed into astable and easy to utilize form, and as one of such processes, there isa process of producing a carotenoid emulsion.

According to the present invention, an emulsion containing a carotenoidas an effective ingredient can be produced with the total all trans-formproportion of the carotenoid maintained high, with good productivity,conveniently, and industrially advantageously.

1. A process for producing a carotenoid emulsion which comprises heatinga suspension of the carotenoid in toluene to a temperature in the rangeof 50 to 120° C., by passing the suspension through a heated conduit fora residence time in the range of 10 to 600 seconds, to dissolve thecarotenoid, immediately mixing the resulting solution with water of atemperature in the range of 5 to 60° C. in the presence of an emulsifierto emulsify the solution and then distilling off the toluene underreduced pressure.
 2. The process according to claim 1, wherein theparticle size of the carotenoid is 50 μm or less.
 3. The processaccording to claim 1, wherein the use quantity of the carotenoid to thetoluene is in the range of 0.1 to 10% by mass.
 4. The process accordingto claim 1, wherein the suspension of the carotenoid contains anantioxidant.
 5. The process according to claim 1, wherein the course ofthe solution from the outlet of the heated conduit to immediately beforethe mixing with the water is also formed with a conduit.
 6. The processaccording to claim 1, wherein the inside diameter of the conduit is inthe range of 0.1 to 500 mm.
 7. The process according to claim 1, whereinthe thickness of the conduit is in the range of 0.1 to 10 times theinside diameter of the conduit.
 8. The process according to claim 1,wherein the length of the heated conduit is in the range of 0.1 to 20 m.9. The process according to claim 1, wherein the length of the conduitfrom the outlet of the heated conduit to immediately before the mixingwith the water is in the range of 0.01 to 20 m.
 10. The processaccording to claim 1, wherein the emulsifier is at least one selectedfrom the group consisting of a fatty acid ester of ascorbic acid, asucrose fatty acid ester, a sorbitan fatty acid ester and a polyglycerolfatty acid ester.
 11. The process according to claim 1, wherein the useamount of the emulsifier is in the range of 0.1 to 5% by mass of thewater used.
 12. The process according to claim 1, wherein the use amountof the water is in the range of 1 to 2,000 times the mass of thecarotenoid.
 13. The process according to claim 1, wherein at least oneselected from the group consisting of gelatin, sugar, gum arabic andstarch is added into the water.
 14. A carotenoid powder obtained byspray drying the carotenoid emulsion obtained by the process accordingto claim 1, or by stirring the carotenoid emulsion in a nonpolar solventto make the emulsion particles, and filtering and drying the particles.